It has hitherto not been possible to produce at low cost, a gas turbine having the properties suitable for operating light vehicles, such as small cars and trucks, light water craft or for simple industrial purposes, viz. a compact design for fitting into a restricted space, and having as satisfactory economy and driving prestanda.
One reason may be that the necessary driving of the compressor has been obtained by making the shaft of the compressor integral with, or connected to the shaft of the single turbine rotor in an inefficient manner. In order to attain a desirable simplicity of design and a reduced cost, it has usually been considered necessary to use a single turbine rotor only.
The acceleration properties of a compressor and turbine, and thus of the car in which the plant is mounted, is not at all acceptable if the speed of the compressor is directly related to the speed of the turbine. Alternatively, a complicated transmission and control device would be required, which is undesirable because it complicates the operation, reduces the efficiency and increases the costs.
The space available within the engine compartment furthermore imposes certain limitations upon the engine structure.